Successful implementation of Ecosystem Based Fisheries Management (EBFM) requires practical methods of translating information on system status into management actions. Threshold values in ecosystem indicators have been demonstrated to provide insight for characterizing change points in marine ecosystems and suggested as reference points for EBFM. We used a guild based multispecies simulation model of the Georges Bank finfish community to quantify tradeoffs and changes among values for proposed ecological indicators given alternative fishing scenarios, and tested the performance of indicator-based approaches for setting system ceilings on annual catches.
Values for ecosystem indicators were sensitive to the exploitation rates on guilds, with total biomass of the community being most sensitive to groundfish exploitation rate. Setting ceilings on system-wide annual catches was successful in constraining values for indicators and revealed levels of system catch associated with indicator change. Community composition indicators showed catch thresholds lower than provided by the total biomass indicator. Ceilings based on community composition indicators more frequently resulted in higher yields and fewer species being overfished than when ceilings were set using total biomass or when no ceiling was in place.
Simulations demonstrated that threshold values in ecosystem indicators could be used to determine reference points in an EBFM context. The broad ranges for threshold values obtained demonstrates the sensitivity of such methods to exploitation history, underscoring the need to both incorporate expert knowledge and relate reference point determination to management objectives.